A comparative study of the seedling leaf oils of the spotted gums: speciesof the Corymbia (Myrtaceae), section Politaria

This study examines variation in seedling leaf oil composition and yield wi thin and between populations of the spotted gum group of eucalypts, with th e aim of better defining relationships between species in this taxonomic gr ouping of economically important forest trees. Eleven provenances from acro ss the geographical distribution, consisting of three provenances of C. mac ulata (Hook.) K. D. Hill & L. A. S. Johnson (syn. Eucalyptus maculata), fou r provenances of C. variegata (F. Muell.) K. D. Hill & L. A. S. Johnson, on e provenance of C. henryi (S. T. Blake) K. D. Hill & L. A. S. Johnson (syn. E. henryi) and three provenances of C. citriodora (Hook.) K. D. Hill & L. A. S. Johnson (syn. E. citriodora) were analysed. Chemometric analysis (PCA and LDA) of oil compositional data gave effective discrimination between a ll four species. The major findings were the clear separation of C. maculat a populations from other members of the group based on chemical composition of their seedling leaf oils. Two chemotypes were identified in C. maculata , one with the cadinol-muurolol complex prominent and a second, less freque nt type in which the eudesmols and elemol were prominent. Corymbia citriodo ra was also unambiguously separated from other group members through the pr esence of citronellal and citronellol in all samples tested, although abund ance of these compounds in individual oils varied between regions of proven ance (north cf. south). The oils from some trees in the southern most prove nance comprised of low levels of these compounds, with an increase alpha -p inene suggesting introgression with C. variegata. The seedling oils of C. v ariegata were mostly dominated by alpha -pinene and several sesquiterpene a lcohols, while the oils of the single population of C. henryi studied were generally low in alpha -pinene and high in sesquiterpenes. Oil composition of C. henryi and the southernmost population of C. variegata showed affinit ies, suggesting intergradation of oil characteristics between these nearby stands. More intensive sampling of C. henryi and C. citriodora and populati ons in the zones of suspected intergradation between C. henryi-C. variegata -C. citriodora would be helpful in clarifying patterns of variation within and between these taxa.